Spark plug



06:74 CROSS REFERENC EXAMINEF March 5, 1935 N. F. sTocKBRlDGl-z Er AL 1,993,388

SPARK PLUG Filed March 29, 1934 Fig. 1.

Patented Mar. 5, 1935 UNITED STATES PATENT OFFICE 1,993,388 SPARK PLUG Norman Frederick Stockbridge, St. Albans, and Douglas Haynes Corbin, Dunstable, England Application March 29, 1934, Serial No. 717,918 In Great Britain March 20, 1933 3 Claims. (Cl. 12S-169) This invention relates to sparking plugs for the bore, whether they be between either the ceinternal combustion engines. ment and the electrode or the cement and the In one type of sparking plug, a central wire insulator, or whether they be within the cement rod electrode is cemented in the bore of an initself. Ii' necessary, as above indicated, heat or 5 sulating sleeve which is usually of a porcelainic other treatment may be applied, after the im- 5 nature. 'I'he quality of the cement employed is pregnation, in order to eiect the sealing by the usually reasonably satisfactory in preventing unliquid. due gas leakage therethrough, and along the bore A satisfactory liquid is a solution of ferrie of the insulating sleeve, and between it and the chloride. It is thought that this, during subsecentral electrode. When, however, the central quent heat treatment, reacts with the traces of 10 electrode is not adhesively secured by the cement sodium silicate in the cement, to form a complex along the full length of the bore of the insulating precipitate which seals the pores and interstices, sleeve, it may happen that undue gas leakage Solutions of water-soluble salts of iron or alumay occur. Undue gas leakage may also occur minum, may be used. In order to bring about l5 owing to cement of an unsuitable character bethe required chemical changes the heat treat- 15 ing employed or to slight irregularities in its ment withthis type of impregnating liquid iniinal structure. volves a temperature of about 100 C.

The object of the present invention is to ren- The impregnation can be effected either hot der gas tight the cement securing a central rod or cold according to the uidity or other nature electrode in the bore of the insulating sleeve of or requirements o! the liquid being used. One 20 a sparking plug. According to the invention the method is illustrated in Fig. 2 of the drawing. set cement is impregnated with an interstice- The insulators, with the central electrode cesealing liquid which forms a sealing precipitate mented in, are mounted in a chamber 5 which with the material of the cement. can be placed in communication by means of a The preferred method is to force a liquid into tap 6 with a vacuum pump 7. By means of a 25 the interstices within the bore of the insulator further tap 8, the chamber can be put into comand subsequently apply heat thereto. Such a munication with a supply tank 9 containing the liquid is one which is capable of permanently impregnating uid. The chamber is rst exsetting and occupying, or of providing a deposit hausted by the pump, and then subsequent to permanently occupying the pores and interstices closure of the tap 6, the tap 8 is opened, where- 30 in the cement, as well as any spaces between the upon liquid rushes into the chamber 5. Due to wall of the bore of the insulating sleeve and the the previous exhaustion of air, the liquid can central wire rod electrode, which .may not be` easily enter the pores and interstices in the incompletely filled with cement. sulators and thus a satisfactory impregnation Further features of the invention will be apis effected. A drain tap 10 allows the chamber 35 parent from the following description taken in 5 to be drained. commotion with the accompanying drawing, in In Fig. 3 of the drawing an alternative method which:- is illustrated. The insulators are clamped, by

Fig. 1 is a longitudinal section of part of a, means of a clamp 1l, in apertures. in the top of 40 spark plug to which the invention is applicable; a chamber 12 such that an air-tight connection 40 Fig. 2 is a diagram of one form of apparatus is obtained between the insulators and the aperfor carrying out the invention; and ture walls. The ends oi' the insulators dip into Fig. 3 is a diagram of another form of appathe mpregnating uid as ShOwn. When the ratos clamp is tightened by means of the wing nut 13,

In Fig. 1 is shown the insulator sleeve 1 of a a PreSSure Dump 14 iS Started up 0I COnneCted 45 'spark plug, which is usually porcelainic in charto the chamber 12, sothat pressure forces the acter, and within the bore of which is the cenuid through the POleS and interste Within tral electrode 2. The electrode is cemented in the central bore of the insulator. the bore in the usual manner by a cement 3, After removal from the impregnating chamber which may be of the sodium silicate type. the insulators are left to ary, and if the huid is 50 In order that the bore of the insulator with the such that further treatment is necessary to cause electrode 2 and cement 3 within it shall be gas a sealing of the pores and interstices, the insutight, the. cement is impregnated with a liquid lators are then subjectedtosuch treatment. For which has the effect of sealing up or fully occuheat treatment they may be placed in a heated Dying the spaces, pores and interstices within chamber or passed through a tunnel oven. 55

We claim:-

1. In the combination an insulator, an electrode in the insulator, cement connecting the electrode to the insulator. said cement being im- 5 pregnated with material filling its pores and forming a sealing precipitate with the material of the cement.

2. A spark plug as defined in claim 1 in which the cement is alkaline and the impregnating material is a metallic salt precipitated by contact with the alkali.

3. A spark plug as dened in claim 1 in which the cement is sodium silicate and the impregnating material is ferrie chloride.

NORMAN FREDERICK STOCKBRIDGE. DOUGLAS HAYNES CORBIN. 

